Copying material for use in electrophotography

ABSTRACT

An electrophotographic copying material having a photoconductive layer formed on the surface of a support, whose back is precoated with an electroconductive layer, with an intermediary layer between said photoconductive layer and the support, said intermediary layer comprising a printing-durable polymer consisting of the reaction product of vinyl polymer, polymer having urethane bonds and water-soluble amino resin.

United States Patent [191 Arai et al.

[ Nov. 27, 1973 COP YING MATERIAL FOR USE IN ELECTROPHOTOGRAPHYInventors: Fumiaki Arai, Tokyo; Wasaburo Ohta; Junji Kurokawa, both ofYokohama; Noriyuki Usui, Kawasaki; Sakae Shimizu, Tokyo; Tetsuo Tanaka,Kasukabe, all of Japan Assignee:

Kabushiki Kaisha Ricoh, Tokyo,

Japan Filed:

June 26, 1972 Appl. No.: 266,147

Related US. Application Data Continuation-in-part of Ser. No. 830,252,June 4, 1969, Pat. No. 3,682,632.

Foreign Application Priority Data June 14, 1968 Sept. 9, 1968 Oct. 2,1968 Oct. 12, 1968 Oct. 9, 1968 US. Cl.

Japan 43/40585 Japan 43/64271 Japan 43/71153 Japan 43/74449 Japan43/73174 101/454, 101/457, 101/462, 117/155 UA, 117/161 KP, 117/161 UN,117/161 UC,

117/161 UB, 260/858, 260/859, 260/885, 260/883 [51] Int. Cl. G033 5/04,603g 5/08 [58] Field of Search 96/1 R, 1.5, 1.6-1.8;

Primary Examiner-Roland Martin, Jr. Attorney-L. Martin Flynn [57]ABSTRACT An electrophotographic copying material having aphotoconductive layer formed on the surface of a support, whose back ispre-coated with an electroconductive layer, with an intermediary layerbetween said photoconductive layer and the support, said intermediarylayer comprising a printing-durable polymer consisting of the reactionproduct of vinyl polymer, polymer having urethane bonds andwater-soluble amino resin.

2 Claims, 1 Drawing Figure PATENTEU NOV 27 I975 TIME (sEc) COPYINGMATERIAL FOR USE IN ELECTROPHOTOGRAPHY CROSS REFERENCE TO RELATEDAPPLICATION This application is a continuation-in-part of our copendingapplication Ser. No. 830,252, filed June 4, 1969, now Pat. No.3,682,632, issued Aug. 8, 1972.

BACKGROUND OF THE INVENTION 1. Field of the Invention The presentinvention relates to an electrophotographic copying material suitablefor both the wetdeveloping process and the dry-developing process, whichhas a photoconductive layer formed on the surface of a support, whoseback is precoated with an electroconductive layer, with an intermediarylayer between said photoconductive layer and the support, saidintermediary layer comprising a printing-durable polymer consisting ofthe reaction product of vinyl polymer, polymer having urethane bonds andwater-soluble amino resin.

2. Description of the Prior Art The conventional electrophotographiccopying material employed for an offset printing plate in the prior arthas been prepared using a paper or fibrous support, one side of which ispreviously processed for electroconductivity, which is provided with anintermediary layer formed by means of coating the opposite side thereofwith a resin solution such as polyvinyl alcohol, polyvinyl acetate,etc., and the surface of thus formed intermediary layer is furthercoated with a dispersion con sisting of a photoconductive substance suchas zinc oxide and the like, a resinous binder such as acryl resin, alkydresin and the like, and a sensitizer, thereby forming a photoconductivelayer. In order to obtain an offset printing plate by employing acopying material as above, the surface of said photoconductive layer isfirst electrified with corona discharge, and then an original opticalimage is exposed onto thus electrified surface to thereby form anelectrostatic latent image, and subsequently a copied image is formedthrough either a drydeveloping process ora wet-developing process, andlastly the non-image areas are made hydrophilic by means of treatingsolution containing inorganic and organic ions.

During the foregoing copying process, the electric potential impressedon the photoconductive layer is required not to easily decay by virtueof conduction by an intermediary layer as well as the support. Suchphenomenon of the potential decay, that is, the so-called dark decay ismuch influenced by the electric efficiency of the intermediary layersuchas electric insulating property, ion property, etc.-as well as physicaland chemical efficiency such as hydroscopicity and the like, while, atthe time of exposure said electric potential is required to decayrapidly. The characteristic curve of said dark decay is desired to bealmost constant under normal humidity or a high humidity anddeterioration thereof under a high humidity should be as little aspossible. Therefore, the back of the copying material is coated with anelectroconductive substance such aspolyvinylbenzyltrimethyl-ammoniumchloride or other surfactant so as tofacilitate the escape of electric charge therefrom. As to the process ofmaking the copying material hydrophilic, inasmuch as a treating solutioncan easily permeate through the photoconductive layer up to theintermediary layer, said intermediary layer is required to have asufficient water-resisting property as well as interlayeror wet-adhesiveproperty. Should a photoconductive layer fail to meet theserequirements, it will result in easy exfoliation in the course of offsetprinting. As to the manufacturing process of a copying material on theother hand, inasmuch as the surface of an intermediary layer is to becoated with a photoconductivelayer-forming dispersion (which employswater or an organic solvent such as to]- uene, etc. as a dispersionmedium), said intermediary layer is required to have an adequatesolvent-resisting property and smoothness of the surface thereof (clayis ordinarily employed as surface-smoothing agent). Since the copyingefficiency (viz. image formability) of a copying material provided withan intermediary layer and the printability of said material whenemployed for an offset printing plate need to meet such requirements asstated above, selection of a material suitable for said inter-layer is amatter of great importance.

However, none of the conventional electrophoto graphic copying materialshas been provided with an intermediary layer capable of satisfying allof these requirements. That is, for instance, a copying materialemploying such a resin as polyvinyl alcohol, polyvinyl acetate, etc. hasbeen attended with defects in respect of water-resisting property,solvent-resisting property, adhesive property or printing endurancethereof and, consequently, has been inadequate as an offset printingplate for use in high volume printing. Therefore, varieties of proposalshave so far been made with a view to remedying these defects. Typicalproposals in this sphere include, for instance, a copying materialhaving an adhesive layer sandwiched in between th intermediary layer andthe photoconductive layer (Japanese Patent No. Showa 40-7332) or acopying material provided with an intermediary layer consisting of areaction product between a polymer having a reactive functional groupsuch as a hydroxyl group, carboxyl group, etc. and an initial-stagecondensate of amino resin (viz. amino-blast) such as trimethylolmelamine and the like (Japanese Patent No. Showa-40-l8708). However, incase of the former of the above cited proposals, the

printability is admittedly improved to some extent, but w it requiresprovision of three layers, to wit, an intermediary layer, an adhesivelayer and a photoconductive layer and, therefore, it is not onlyuneconomical but also apt to give rise to lack of uniformity ofefficiency, while, in case of the latter, it has such a drawback thatthe residual formaldehyde within the intermediary layer is apt tovolatilize to thereby decompose the sensitizer (viz. a dye) contained inthe photoconductive layeror give rise to a change of quality of saidphotoconductive layer with the lapse of time to thereby causedeterioration of preservability as well as degeneration of theelectrostatic properties and printability thereof.

SUMMARY OF THE INVENTION The present invention provides anelectrophotographic copying material having an improved intermediarylayer, with a view to elimination of the above stated shortcomings ofthe copying materials in the prior art and also the provision of acopying material having superb electrostatic properties as well asprinting endurance suitable for the offset printing plate.

As for the intermediary layer according to the present invention, thereis employed a composition comprising the reaction product of vinylpolymer, polymer having urethane bonds and water-soluble amino resin.

Said vinyl polymer includes, for example, a polymer or a copolymercomprising monomers having a polymerizable vinyl radical such as acrylicester, methacrylic ester, acrylonitrile, styrene, vinyl chloride,vinylidene chloride, vinylidene acetate, vinyl acetate, ethylene,butadiene, etc. or a polymer or a copolymer produced by the reactionbetween at least one member of the foregoing monomers having apolymerizable vinyl radical and at least one member of such monomers asacrylic acid, methacrylic acid, maleic acid, succinic acid, itaconicacid, glycidic acid, other carboxylic acids as well as acid anhydridesthereof, glycidyl meth' acrylic acid, hydroxyethylacrylic acid,hydroxypropylacrylic acid or esters thereof, acrylamide, vinyl amideformate and the group of amines such as primary amines, secondaryamines, tertiary amines, etc., said polymer or copolymer having one ormore radicals selected from carboxyl group, alkoxycarbonyl group, aminogroup, amido group, hydroxyl group, alkoxyl group, epoxy group and cyanogroup.

The aforesaid polymer having a urethane bond includes one or morepolymers selected from methylol urethane polymers and other modifiedurethane polymers. Said methylol urethane polymer includes, forinstance, a partial-methylolurethane polyvinylalcohol (manufactured byToyo Koatsu Kogyo Co., Ltd. and sold under the name URAMINE-XP 72,URAMINE-T I000, URAMINE-T 1050 and URAMINE-XP66) which is obtained bydenaturing polyvinyl alcohol into urethane. There being somecommercially available polymers containing water-soluble amino resin asabove, it may be advisable to utilize them for the present invention. Apartial-methylolurethane polyvinl alcohol has a methylol group bonded atthe end of the polyvinyl alcohol moiety, so that it has plenty ofreactivity as compared with an ordinary polyvinyl alcohol. It is notonly provided with self-bridgemaking property but also is capable ofreadily reacting with vinyl polymer and water-soluble amino resin..Moreover, the reaction products thereof have complex network structuresand, consequently, are excellent in water resistance as well as solventresistance.

The foregoing water-soluble amino resin includes alkylatedmelamine-formaldehyde resin such as melamine or dimethylol melamine,trimethylol melamine, etc., ureaformaldehyde resin, aniline-formaldehyderesin, cyanamide-formaldehyde resin or mixtures of these resins.According to the present invention, mixing of quite a small amount ofsaid amino resin suffices to effect the object thereof, and will providethe intermediary layer with an appropriate flexibility as well as asatisfactory smoothness which could not be expected of any copyingmaterial in the prior art.

In case of forming an intermediary layer by employing the aforesaidvinyl polymer of water-dispersible quality, it is only necessary to takesuch steps that a film-formable dispersion is first prepared bydispersing a vinyl polymer, a polymer having a urethane bond and awater-soluble amino resin polymer in water, ammonium chloride or thelike is then added to said dispersion as a bridge-making catalyzer, andthe resultant solution is coated on a support and dried at l l-140C for1-2 minutes subsequent thereto.

As for said dispersion for use in forming an intermediary layer, itcomprises (a) 1 part by weight of vinyl polymer, (b) 0.1-5 parts byweightpreferably 0.1-2

parts by weight--ofa polymer having a urethane bond, and (0) 005-05parts by weight of a water-soluble amino resin per 1 part by weight ofthe sum of the foregoing two polymers (a) plus (b). Further, on theoccasion of forming said intermediary layer, polyvinyl acetate,thermoplastic acrylic resin or the like may be jointly employed in orderto further improve the flexibility as well as the adhesive property ofsaid layer towards the photoconductive layer.

BRIEF DESCRIPTION OF THE DRAWING The accompanying drawing is a graphshowing the respective dark-decay properties of two copying materialsaccording to the present invention and a control copying material forcomparisons sake.

DESCRIPTION OF THE PREFERRED EMBODIMENTS This invention will be furtherdescribed with reference to the following illustrative Examples.

EXAMPLE I An intermediary-layer-forming dispersion consisting of:self-bridging type acrylic resin emulsion (a manufacture of Nippon AcrylChemical Industries Co., Ltd. sold under the name I-IA 16, containing 45wt. percent of resin) parts by weight acrylic ester emulsion (PRIMAL-AC22, containing 45 wt. percent of resin) 42 parts by weightpartial-methylolurethane polyvinyl alcohol (a manufacture of Toyo KoatsuIndustrial Co., Ltd. sold under the name URAMIN-XP 66, containing 10 wt.percent of resin) 450 parts by weight urea-formaldehyde resin (amanufacture of Toyo Koatsu Industrial Co., Ltd., sold under the nameURAMIN-P2200 containing 48 wt. percent of resin) 19 parts by weightammonium chloride 1.1 parts by weight water 300 parts by weight wascoated on the surface of a slick paper (pulp ratio of N/L being 50/50)by means of an air-doctor and was dried for 1 minute at C, whereby anintermediary layer of 6p. thick was formed.

Subsequently, an electroconductive-layer-forming dispersion consistingof:

self-bridging type acrylic resin emulsion 100 parts by weightpartial-methylolurethane polyvinyl alcohol (a manufacture of Toyo KoatsuIndustrial Co., Ltd. sold under the name URAMIN-XP 66) 90 parts byweight urea-formaldehyde resin (named 2200) 11 parts by weightpolyvinylbenzyl-trimethylammonium chloride (containing 30 wt. percent ofresin) 10 parts by weight ammonium chloride 1 parts by weight water 300parts by weight was coated on the back of the foregoing slick papersupport and was dried for l minute at 140C, whereby an electroconductivelayer was formed on said support. Both the intermediary layer and theelectroconductive layer formed as above proved to be a perfect resinfilm having a smooth surface free of any flaw or pinhole.

Next, a photoconductive-layer formable acrylic resin was prepared bycausing a mixture comprising 50 parts URAMIN-P by weight of styrene, 47parts by weight of butyl acrylate, 3 parts by weight of acrylic acid and100 parts by weight of toluene to react for hours at 100C. Then, adispersion was prepared by dispersing 40 parts by weight of said acrylicresin, 100 parts by weight of zinc oxide and 2cc of 5 percent methanolsolution of Rose Bengal in 150 parts by weight of toluene, and same wascoated on the surface of the foregoing intermediary layer of the supportand dried for 1 minute at 150C to thereby form a photoconductive layerof 12p. thick, whereby a desired electrophotographic copying materialwas obtained. 7

After that, the surface of the thus formed photoconductive layer of saidcopying material was subjected to corona discharge under the conditionsof 32C and a relative humidity of 80 percent to impart a saturatedpotential, and, after 30 seconds, the electrified surface was exposed tolight and the dark-decay characteristic curve was sought.

On the other hand, a control electrophotographic copyingmaterial for usein comparison was prepared in just the same way as the present exampleexcept that the principal components of the intermediary layer andelectroconductive layer thereof were replaced by the reaction productsbetween the initial-stage condensate consisting of dimethyl-trimethylolmelamine resin and styrene-hexyl acrylate-acrylonitrile, and the darkdecay characteristic curve was sought under the same conditions. Theresults of experiments as above were as shown in the accompanyingdrawing. In said drawing, curve 1 shows the characteristic in case ofthe present example, while curve 3 shows the characteristic in case ofthe comparative material. (Curve 2 shows the characteristic in case ofExample 2). As may be understood from said diagram, the copying materialaccording to the present invention is provided with a saturatedpotential higher than that of said material employed for comparisonssake, the decrement of the dark decay characteristic curve thereof isslight, and the sensitivity thereof is very high. Accordingly, thecopied image obtained through dry development as well as wet developmentof a copying material of the present invention was very clear.Furthermore, in case where the copied image obtained through drydevelopment was employed for an offset-printing plate, it was not erodedby etching liquid or immersion water, and could turn out quiteacceptable prints even after more than 10,000 prints were produced.

EXAMPLE 2 a. A mixture comprising:

methyl methacrylate 4 60 parts by weight ethyl acrylate 45 parts byweight acrylamide 2 parts by weight glycidyl methacrylate 3 parts byweight ammonium persulfate 0.2 parts by weight sodiumlaurylbenzenesulfonate 1.0 parts by weight hydroxyethyl cellulose 0.5parts by weight water 100 parts by weight was caused to react for 6hours at 120C, whereby a vinyl-polymer emulsion was prepared.Subsequently, a dispersion was prepared by dispersing 100 parts byweight of said emulsion, 500 parts by weight of partialmethylolurethanepolyvinyl alcohol solution (a manufacture sold under the name URAMlN-T1000,

' containing 10 wt. percent of resin), 40 parts by weight ofthermoplastic acryl resin emulsion (a manufacture sold under the namePRlMAL-AC 22, containing 50 wt. percent of resin), 8 parts by weight ofmelamineformaldehyde resin (a manufacture of Sumitomo Chemical Co.,Ltd., sold under the name SUMIREZ Resin 613 containing wt. percent ofresin) and 1.4 parts by weight of ammonium chloride to parts by weightof water. The thus prepared dispersion was then coated on one side of aslick paper (pulp ratio of N/L: 50/50, thickness: p.) by means of anair-doctor and was dried for 1 minute at C, whereby there was formed anintermediary layer of 6p. thick.

Next, another dispersion was prepared by dispersing 100 parts by weightof the emulsion obtained through the process as set forth under (a)above, 90 parts by weight of the foregoing partialmethylolurethanepolyvinyl alcohol solution, 5 parts by weight of the foregoingthermoplastic acryl resin emulsion, 17 parts by weight of 30 percentaqueous solution of polyvinylbenzyl-trimethylammonium chloride, 1.4parts by weight of ammonium chloride, 80 parts by weight of clay and 0.3part by weight of sodium hexametaphosphate to 200 parts by weight ofwater, and the thus prepared dis persion was coated on the other side(viz. uncoated side) of said slick paper support in the same way as inthe case of forming the aforesaid intermediary layer and was dried for 1minute at 140C, whereby an electroconductive layer was formed. Then, thesurface of said intermediary layer formed on the support was dipped for1 hour in toluene to be employed on the occasion of forming aphotoconductive layer subsequent thereto, but there was observed nochange at all.

Subsequently, by means of employing the sameelectrophotoconductive-layer-formable dispersion and in the same way asin Example 1, a photoconductive layer of 12p. thick was formed and adesired electrophotographic copying material was prepared therefrom.

The surface of the photoconductive layer of the thus obtainedelectrophotographic copying material was subjected to corona dischargeat 32C under the conditions of 32C and 80 percent R.1-l. as in the caseof Example l to seek its dark decay characteristic curve (See curve 2 ofthe accompanying drawing), and the thus obtained characteristic curvewas compared with the curve 3 pertaining to the control copying materialemployed for comparisons sake. As a result, it was found that thecopying material of the present example could be provided with such ahigh saturated potential as in the case of Example 1 and the decrementof its dark decay characteristic curve was slight and the sensitivityEXAMPLE 3 b. A mixture comprising:

methyl methacrylate 60 parts by weight butyl acrylate 30 parts by weighthydroxyethyl acrylate 10 parts by weight ammonium persulfate 0.2 partsby weight sodium laurylbenzene sulfonate 1.0 parts by weighthydroxyethyl cellulose 0.5 parts by weight water 100 parts by weight wascaused to react for 6 hours at 120C, whereby a film-coating copolymeremulsion was prepared. Next, a dispersion was prepared by dispersing 100parts by weight of said emulsion, 40 parts by weight of vinyl acetateemulsion (containing 50 wt. percent of resin), 180 parts by weight ofpartial-methylolurethane polyvinyl alcohol solution (viz. a solutioncomprising 25 wt. percent of resin, and named URAMlN-XP 72) whichcontains 10 wt. percent of urea-formaldehyde resin and 1.4 parts byweight of ammonium chloride to 100 parts by weight of water. The thusprepared dispersion was then coated on a slick paper (pulp ratio of N/L:50/50, thickness: 120) in the same way as in Example 1 and was dried,whereby an intermediary layer of 6p. thick was formed. After that,another dispersion was prepared by dispersing 100 parts by weight of theemulsion obtained through the process as set forth under (b) above, 40parts by weight of the foregoing partialmethylolurethane polyvinylalcohol solution containing said urea-formaldehyde resin, 1 17 parts byweight of 30 percent aqueous solution ofpolyvinylbenzyltrimethylammonium chloride, 1.4 parts by weight ofammonium chloride, 80 parts by weight of clay and 0.3 part by weight ofsodium hexametaphosphate to 200 parts by weight of water, and the thusprepared dispersion was coated on the other side (viz. non-coated side)of said slick paper support and was dried for 1 minute at 140C, wherebyan electroconductive layer was formed.

Then, the surface of said intermediary layer formed on the support wascoated with the same photoconductive dispersion as in the case ofExample 1 and was dried for 1 minute at 130C, whereby a desiredelectrophotographic copying material provided with a photoconductivelayer of 10p. thick was obtained.

The thus prepared copying material demonstrated almost the samecharacteristics as that of Example 1 and, when employed for anoffset-printing plate, was stable against etching liquid as well asimmersion water,

and showed no deformation or damage even after producing more than10,000 prints.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. In an electrophotographic copying material comprised of anelectroconductive paper support, an intermediate layer and aphotoconductive layer containing photoconductive zinc oxide, theimprovement wherein said intermediate layer consists essentially of thereaction product of (1) vinyl polymer selected from the group consistingof (A) a polymer or copolymer of at least one monomer selected from thegroup consisting of acrylic ester; methacrylic ester; acrylonitrile;styrene; vinyl chloride; vinylidene chloride; vinylidene acetate; vinylacetate; ethylene; and butadiene, and (B) a copolymer of at least one ofsaid monomers with at least one comonomer selected from the groupconsisting of maleic acid, succinic acid, itaconic acid, glycidic acidand acid anhydrides of the foregoing acids; gylcidyl methacrylic acid,hydroxyethyl-acrylic acid, hydroxypropylacrylic acid and esters thereof;acrylic acid; methacrylic acid; acrylamide; vinyl amide formate; primaryamines; secondary amines; and tertiary amines, (2) partialmethylolurethane polyvinyl alcohol and (3) at least one water-solubleamino resin selected from the group consisting of melamine, dimethylolmelamine, trimethylol melamine, urea-formaldehyde resin,aniline-formaldehyde resin and cyanamideformaldehyde.

2. An electrophotographic copying material as claimed in claim 1 inwhich said intermediate layer consists essentially of a. one part byweight of vinyl polymer, b. from 0.1 to 5 parts by weight of partialmethylolurethane polyvinyl alcohol, and c. from 0.05 to 0.5 parts byweight of water-soluble amino resin, per 1 part by weight of the sum of(a) plus (b).

PRINTER'S TRIM L :Attesting Officer v UNITED STATES PATENT OFFICECERTIFICATE OF CORRECTION 3 775 108 Dated November 27, 1973 FnmiakiArai, Wasaburo Ohta, Junji Kurokawa, Noriyuki Usui, Sakae Shimizu andTetsuo Tanaka Patent No.

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Under the heading "Foreign Application Priority Data" change "Sept. 9,1968 Japan 43/64271" to 9 I 0 l o c o c o o u u o I o o n o a o I n 77 oSigned and sealed this 23rd day of April'lWLt.

(SEAL) Attest:

O. MARSHALL .DANN

EDWARD 'I"'i..FLETUlfi-JR,JR.

Commissioner of Patents

2. An electrophotographic copying material as claimed in claim 1 inwhich said intermediate layer consists essentially of a. one part byweight of vinyl polymer, b. from 0.1 to 5 parts by weight of partialmethylolurethane polyvinyl alcohol, and c. from 0.05 to 0.5 parts byweight of water-soluble amino resin, per 1 part by weight of the sum of(a) plus (b).